This invention relates to a fluid seal, preferably a liquid seal, to seal a gas or a liquid in for instance hydraulic cylinders, pneumatic cylinders or hydropneumatic cylinders. In an embodiment of present invention a seal has been described which can be divided in two major components. The first component will be referred to as the “surface tension seal”, while the second will be referred to as the “pressure divider”.
The operation principle of the surface tension seal is comparable to that of sealing rubber O-rings but the seal ring is made of a fluid instead of rubber. A liquid O-ring for instance resists the actuation pressure relying on surface tension forces. These O-rings can be linked in series, hereby increasing the maximum seal pressure.
The pressure divider is a system that generates a pressure drop by means of an hydraulic equivalent system to an electric voltage divider. The pressure divider is located before the surface tension seal and performs the first pressure drop. The main advantage of combining these two systems is that the surface tension seal is able to reduce the leakage to zero and that the pressure divider is able to perform a large pressure drop. Nevertheless, the surface tension seal can also create a considerable pressure drop. This means that in applications where the seal pressure of the surface tension seal is not exceeded, the pressure divider can be omitted. However, omitting the pressure divider will always result in tighter tolerances when manufacturing the seal.
The presented seal technology is most interesting for micro devices since surface tension is one of the strongest forces at microscale. In addition, the described seal is easy to miniaturize since no complex components are needed. The presented seal offers for instance a solution for the sealing of pneumatic actuators, of hydropneumatic actuators or of hydraulic actuators and is in particular interesting for hydraulic microactuators since the maximum seal pressure scales inversely proportional to size and the seal can be manufactured as one monolithic part with the actuator cylinder.
An hydraulic actuator suitable for present invention can for instance hydraulic cylinders or hydraulic clamp cylinders as for instance made available to the public by companies such as MICO, AHP Merkle, LJM Hydraulik, Spx Fluid Power, Amf Andreas Maier, Atos, De-Sta-Co, Douche Hydro, Duplomatic, Oleodinamica, Duplomatic, Eaton—Hydro Line, Eaton—Vickers, Glual Hidraulica, Regnier, Rexroth—Industrial Hydraulics, Ljm Hydraulik. Hydraulic actuators suitable for present invention can also be linear cylinders, hydraulic light-alloy cylinders, single-acting and double-acting hydraulic actuators, aluminum hydraulic cylinders, flat cylinders, hollow piston cylinders, telescopic hydraulic cylinders, hydraulic locking cylinders for injection molding machines, hydraulic pancake lock-nut cylinders, pancake lock nut cylinders, hydraulic rotary actuators, rotary cylinders, hydraulic servo-cylinders, lock-nut hydraulic cylinders, as for instance been produced by Ds Dynatiec, Eckart, Olaer Industries, HKS, Montanhydraulik, Atos, Glual Hidraulica, Enerpac, Ljm Hydraulik and Hidraulica Um Plopeni. Also Pneumatic cylinders or hydropneumatic cylinders from Farger & Joosten or Eckart, water hydraulic cylinders from LJM Hydraulik and tie rod hydraulic cylinders from Eaton—Hydro Line or Universal Hydraulik and mini-hydraulic cylinders from Hunger Hydraulik ca be suitable for present invention.
The surface tension seal of present invention is particularly suitable for microdevices. During the last decades several scientific studies focused on the choice of appropriate actuation technologies for microdevices. Especially electrostatic and electromagnetic motors were investigated. However, recent research shows that hydraulic systems develop a higher force, work and power density at micro scale (Bütefisch S., et al. Sensors and actuators A, 2002, 638-645; Binnard, M., Leg Design for a Small Walking Robot, Master's thesis MIT, 1995, Wapner P., Hoffman W., Sensors and actuators B, 2000, 52-60 and Peirs J., et al., Sensors and Actuators A, Vol. 85, 2000, 409-417).
Microhydraulic systems have for instance been described in N. R. Tas, T. S. J. et al. Pages: 174-177 Nanotech 2002 Vol. 1 and fluidic microdevices have for instance been described in Harley, J. et al. 1989, Proc. IEEE pp. 25-28; Kricka, L, et al. 1989, “Liquid Precision Engineering and Optomechanics Vol. 1167, pp. 159-168 and Pfahler, J., et al. 1990, Sensors and Actuators, Vol. A21-A23, pp. 431-434 and micropneumatic systems have for instance been described in Bütefisch S et al Sensors and actuators A, 2002, 638-645.
Despite these promising properties, hydraulic actuators are rare in Micro Systems Technology (MST) because of inherent sealing difficulties. Most existing miniature hydraulic actuators suffer from either leakage or high friction. These problems are due to the fact that the typically used rubber O-rings or lip seals are not appropriate for micro devices. The main technological barrier for the development of such micro actuators is the lack of an appropriate sealing technology.
Thus, there is a need in the art for a novel for low friction seal. The present invention solves the problems of the related art by replacing traditional rubber O-rings for instance by a fluid O-rings, preferably by a liquid O-ring. The latter resist the actuation pressure relying on surface tension forces. A seal in accordance with this invention has a number of advantages. Due to the use of a surface tension seal, the solid-solid contact between the seal and the moving part can be avoided. Therefore, friction and seal wear can be reduced substantially. If the applied pressure does not exceed its designed value, there will be no leakage. This is an important property for all applications that need a hermetic seal. Furthermore, this seal is easy to miniaturize and opens new prospective for the sealing of fluidic microdevices. The technology of present invention can also be used in any other applications where a low leakage, a low friction or both are desired as for instance in precision mechanics.
Besides high seal pressures, an important advantage of this technology are that the solid-solid contact between the seal and the moving part can be avoided and consequently, friction and seal wear can be reduced substantially.
Typical applications for this microactuator are process automation, inspection and minimally invasive surgery.